For recording onto optical information recording media such as CD-R or DVD-R (hereinafter referred to as “media” or a “medium”), the compatibility between a medium to be recorded on and a device to be use for recording (hereinafter referred to as a “drive”) depends on each combination of them. This may be caused by the medium side factor wherein the optimum recording condition is varied by the difference in a recording material comprising the medium or the film formation variation during production, or by the drive side factor wherein the optimum recording condition is varied by the difference in a pickup device and/or a semiconductor laser comprising the drive or assembly variation during production. In fact, a suitable recording condition exists for each combination of a medium and a drive due to the combination of those factors.
Accordingly, in a conventional method, ID information on a medium type identifiable by a drive is stored in the medium as well as a recording condition prepared for each medium type is stored in the drive. When recording is actually performed, the ID information stored in the medium is read from the medium loaded to the drive, and a recording condition related to the ID information is used.
However, in the conventional method, suitable recording conditions can be selected for pre-verified known media, but prepared recording conditions may not be adequate to accommodate unknown media that are not pre-verified. Further, depending on the changes in the recording environment such as a recording speed, disturbance, and change over time, the prepared recording conditions may not be adequate even for known media.
A method contemplated to accommodate such an unknown medium is described in the following literatures:
Patent Document 1: Japanese Unexamined Patent Publication No. 2003-30837, and
Patent Document 2: Japanese Unexamined Patent Publication No. 2004-110995
As described in the paragraph [0020] of the Patent Document 1 as “ . . . a phase error relative to a channel clock is detected for every recording pattern. A recording compensation parameter adjustment section 12 optimizes an emission waveform rule on the basis of the detection result at the phase error detection section 11, ” a method of detecting a phase error by comparing with a channel clock and of correcting the phase error is disclosed.
Also, the paragraph [0024] of the document describes that “Next, a test pattern for determining an emission waveform rule is recorded. The area wherein the test pattern is recorded is reproduced, and the relationship between a prepared emission waveform rule and a phase error amount is examined. In other words, the phase error amount in the combination of the length of each mark and the length of each space immediately before the mark is measured. An emission waveform rule wherein the phase error amount becomes zero is estimated from the measured phase error amount, whereby a desired emission waveform rule is determined . . . ”, disclosing a method for measuring a phase error amount for every combination of a mark and a space, and then estimating an emission waveform rule wherein the phase error amount becomes zero (see FIGS. 8 and 12).
The method disclosed in the Patent Document 1 is effective for optimizing a strategy because a correction is made based on a phase error of a recording pattern.
However, because the method disclosed in the Patent Document 1 involves, as conventional methods, a fine adjustment of a prepared strategy stored in a drive, it is difficult to provide a favorable recording quality for media to which prepared strategies are not applicable.
Also, the paragraph [0045] of the Patent Document 2 describes that “ . . . a top pulse corresponds to a 3T period and a non-multipulse corresponds to a 8T period are generated integrally (consecutively) . . . ” and the paragraph [0046] of the document describes that “ . . . the laser power for a write pulse is adjusted in two levels, and when the ratio between a laser power (a height value of the top pulse) Ph and a laser power (a height value of the non-multipulse) Pm is optimum, an optimum power can be obtained . . . ”, suggesting the effectiveness of optimizing the Ph/Pm ratio.
However, in the method disclosed in the Patent Document 2, as described in the paragraph [0067] of the document, the initial values of Ph and Pm are temporarily set based on values stored in a drive or a medium, and then the Ph/Pm ratio is calculated. Accordingly, as in the case of the Patent Document 1, it is difficult to provide favorable recording quality for media to which the temporarily set values are not applicable.
Further, recording information onto an optical information recording medium such as an optical disk is performed by modulating recording data by EFM (Eight to Fourteen Modulation) method or 8-16 modulation method; forming recording pulses based on the modulated signal; controlling the intensity and irradiation timing of a laser beam based on the recording pulses; and forming recording pits on the optical disk.
Since the formation of recording pits involves using the heat generated by laser beam irradiation, the recording pulses require some configuration in consideration of the heat accumulation effect and heat interference. Thus, in conventional methods, recording onto an optical disk has been performed by setting various parameters, which configure the recording pulses, for each kind of optical disks in the form of strategy, and then selecting one of those strategies that is the most suitable for the recording environment of the disk.
This strategy depends, for instance, not only on variation between optical information recording devices such as variation in spot diameter or in mechanical accuracy depending on a pickup device, but also on the manufacturer, type and recording speed of a optical disk used for recording/reproducing. Consequently, setting an optimum strategy improves recording quality.
For this reason, a method has been proposed, wherein a strategy for each of optical disk types produced by different manufacturers is determined and pre-stored in a memory, and when recording information onto an optical disk, information of the optical disk type is read from the optical disk, and retrieve the optimum strategy that corresponds to the optical disk type from the memory, followed by using it.
However, although the above-mentioned method enables optimum recording for optical disk types produced by different manufacturers that are pre-stored in the memory, it cannot provide optimum recording onto a medium of which a manufacturer and a type are not pre-stored in the memory. In addition, optimum recording may not also be provided even for the optical disk types pre-stored in the memory when a recording speed is varied.
Consequently, as described in the following Patent Documents 3 to 6, a number of methods are suggested, wherein various optical disks can be supported by performing a test recording for each recording, whereby an optimum strategy may be determined:
Patent Document 3: Japanese Unexamined Patent Publication No. 1993-144001,
Patent Document 4: Japanese Unexamined Patent Publication No. 1992-137224,
Patent Document 5: Japanese Unexamined Patent Publication No. 1993-143999, and
Patent Document 6: Japanese Unexamined Patent Publication No. 1995-235056
However, since the methods disclosed in the Patent Documents 3 to 6 require test recording before information recording is started, a strategy cannot be corrected at the same time as recording, making it difficult to accommodate the case where the optimum condition is varied for inner and outer circumferences of an optical disk to be used.
Since an optical disk has slightly different recording characteristics for its inner and outer circumferences and a recording device may have different recording speeds for the inner and outer circumferences, a technique that involves adjusting laser power to reduce the difference between the inner and outer circumferences is disclosed in the following Patent Document 7 as a method to solve the problem of the variation in recording quality for inner and outer circumferences:
Patent Document 7: Japanese Unexamined Patent Publication No. 1978-050707.
The Patent Document 7 discloses a method wherein the optimization of a laser power is automatically performed by detecting the change in light intensity of an auxiliary beam, which is called OPC (Optimum Power Control).
The OPC described above is called Running OPC that adjusts the power in real time. Since correction parameters can be determined based on statistical indicators such as asymmetry values, real time correction that performs adjustments at the same time as recording becomes possible. However, when correcting a pulse width and/or pulse phase condition, because detecting the shift amount between a recording pulse and the corresponding pit formed on an optical disk is required, the conventional OPC may not be used.
Accordingly, the realtime adjustment of pulse conditions requires a technology to detect the positions and lengths of pits and spaces at the same time as recording. As one of the approaches to meet this requirement, the following Patent Document 8 discloses a technology that reproduces positions approximately same as the recording positions:
Patent Document 8: Japanese Unexamined Patent Publication No. 1976-109851.
However, although this method is applicable to optical magnetic recording, it is difficult to apply to optical recoding without the use of magnetism. That is, the laser power is not modulated in optical magnetic recording because modulating magnetism yields information recording. However, in optical recording, modulating laser power yields information recording, and the effects of the modulation arise when reproducing.
As the solution for the above problem, methods disclosed in the following patents documents are known:
Patent Document 9: Japanese Unexamined Patent Publication No. 1989-287825,
Patent Document 10: Japanese Unexamined Patent Publication No. 1995-129956,
Patent Document 11: Japanese Unexamined Patent Publication No. 2004-220044, and
Patent Document 12: Japanese Unexamined Patent Publication No. 1997-147361.
The Patent Document 9 discloses a technology wherein separate laser beams are irradiated at non-recording area and recording area respectively, and a reproduction signal is retrieved from the separated signals by dividing them. According to this method, the distortion in a reproduction signal waveform due to the light intensity modulation of a laser beam during recording information can be corrected.
The Patent Document 10 discloses a technology of obtaining a reproduction signal by offsetting a modulated power with the opposite phase clock of a laser power appropriately amplified by AGC (Auto Gain Control).
The Patent Document 11 discloses a technology that offsets the distortion in a reproduction signal associated with the waveform variation in recording pulses by generating a signal that corresponds to the waveform variation in recording pulses using a delay inversion equivalent circuit.
Each of the methods disclosed in Patent Documents 9 to 11 is a technology that offsets modulated components by operations, and the offset is theoretically available. However, there remain various problems in practical applications in terms of accuracy of the offset and operation speed.
The Patent Document 12 discloses a technology that detects the distortion in recoding state in realtime by inputting delayed pulses generated by delaying pulses used for recording into a phase comparator along with reproduction pulses using a gate signal generated by inverting a modulated signal.
However, since the method disclosed in the Patent Document 12 involves the reproduction of pits while the recording pulse is off, when the power of a sub beam is low, it is difficult to obtain satisfactory quality of a reproduction signal. Especially in a configuration wherein a reproduction sub beam is branched from a main beam for recording, it is difficult to allocate adequate power to the sub beam when branching ratio is 20:1 or 30:1.
The branching ratio described in the Patent Document 12 is 8:1, but since the branching ratio tends to be larger as recording speed increases, and further, since beam power while recording pulse is off is normally 1 mW and below, the intensity of reflected light from a recording surface that is detectable while recording pulse is off becomes significantly small. When the light intensity becomes smaller, a favorable detection signal may not be obtained because noises such as a circuit noise or a media noise disturbs the detection of the signal.
On the other hand, the integral detection method that uses integration value of a reproduction RF signal, the amplitude detection method that uses 1 st derivative value of an RF signal, or the peak detection method that uses 2nd derivative value of an RF signal is known as a method of detecting pits and space lengths recorded on a optical disk.
However, in an optical recording device wherein reproduction is performed using a laser beam having a relatively shorter wavelength, since reflected beams from a spot and a pit in an optical medium recorded at lower density are not interfered by each other, it is difficult to detect length information by the integral detection method of an RF signal.
In the method that uses 1st derivative value of an RF signal, when recording power changes as recording speed varies, a signal binarized at the same slice level provides two different length for a pit and a space respectively that should have the same length. As a solution for this problem, a method that involves changing a slice level according to a recording speed may be effective, but setting an appropriate slice level for each recording speed is not easy.
As the peak detection method that uses 2nd derivative values of an RF signal, for instance, the method disclosed in the following patent document is known:
Patent Document 13: International Publication No. WO96/24130.
The method disclosed in the Patent Document 13 suggests that differentiating the difference signal (i.e. a tangential push-pull signal) from a photodetector that is divided into two areas by a parting line that is optically vertical to a rotational direction of an optical medium generates a signal equivalent to a 2nd derivative value of an RF signal, whereby edge positions of pits can be detected.
However, when the method disclosed in the Patent Document 13 is used to detect pits and spaces recorded on a high-density type optical disk, such as a DVD-class medium, errors in the derivative value of a tangential push-pull signal for shorter pits and spaces such as 3T or 4T that are likely to be interfered may arise, resulting in detecting values different from the actual pits and spaces lengths.
On the other hand, the following Patent Document 14 discloses a method for improving the above-mentioned Running OPC:
Patent Document 14: Japanese Unexamined Patent Publication No. 2002-117544.
The Patent Document 14 discloses a method of detecting an optimum power using certain pit/land pattern, but since the pit/land pattern described in the document cannot distinguish an adjustment parameter for a power from that for a pulse width, a margin sufficient to meet good recording quality may not be ensured, resulting in the difficulty in accommodation of high-speed recording.
It is therefore the object of the present invention to provide a method to optimize recording conditions for various media that have different recording characteristics for their inner and outer circumferences.